It's my Catholic up bringing that takes me there, Meself. There is just no way that Mr. Kavanagh (poetic license or none) would ever refer to an Angel in anything but a masculine term. Couldn't happen.
I take the line to mean that for an Angel to stoop down to loving an earthly being such as himself would be grounds for sudden departure from the heavens.
The bestowing of heavenly qualities upon a human being was sacriligeous enough to satisfy even Patrick Kavanagh but to refer to himself as an angel would just make no sense. Trust me on this one. I'm right, once in a while.